Emitted flux λ = 1.3 mm as a function of the 68 (left) and 95% (right) flux radius, similar to Fig. 4, for low-angular momentum discs with strong viscous heating. These discs show smaller radii at a given flux than the high-angular momentum, weakly viscously heated discs from Fig. 4. At the same time, they produce too high fluxes and too low radii when compared to the class 0/I sample. The red star shows the disc around R CrA IRS7B-a, which has signs of active viscous heating (Takakuwa et al. 2024).